Date of Award
Doctor of Philosophy (PhD)
Physics and Astronomy
Dr. Marco Ajello
Dr. Daniel Castro, co-advisor/co-chair
Dr. Joan Marler
Dr. Dieter Hartmann
Pulsar wind nebulae are highly magnetized particle winds, descending from core collapse supernovae (CC SNe), and each powered by an energetic, rapidly rotating neutron star. There are at least 125 Galactic pulsar wind nebulae (PWNe) that have been discovered from radio wavelengths to TeV gamma-rays, the majority of which were first identified in radio or X-ray surveys. An increasing number of PWNe are being identified in the TeV band by ground-based air Cherenkov Telescopes such as HESS, MAGIC, and VERITAS such that they constitute the dominant source class of Galactic TeV emitters. High-energy sources like PWNe may be responsible for producing the bulk of Galactic cosmic rays (CRs) with energy up to E ~ 10^(15) eV. Combining available MeV-GeV data with observations in the TeV band is critical for precise characterization of high-energy emission from the relativistic particle population in PWNe, thus revealing the capability to produce a significant fraction of the detected Galactic CR flux. However, MeV-GeV PWN counterparts are still largely lacking even after 12 years of continuous observation of the entire sky. Less than a dozen PWNe are currently identified by the Fermi-LAT in the MeV-GeV band. Most PWNe are located along the Galactic plane embedded within the prominent, diffuse Galactic gamma-ray emission, which makes these sources difficult to disentangle from the bright diffuse background. Moreover, nearly 300 rotation-powered pulsars that are capable of generating PWNe can also emit brightly in the Fermi-LAT gamma-ray band, potentially outshining and obscuring their fainter PWNe. The capability to identify more gamma-ray PWNe is greatly improved by the recent upgrades in the event processing of the Fermi-LAT data, which provides better spatial resolution and sensitivity of the instrument. Taking advantage of the recent upgrade, we present a systematic search for gamma-ray counterparts to known PWNe in the 300MeV - 2TeV energy band using 11.5 years of Fermi-LAT data. For the first part of this search, we target the locations of PWNe previously identified across the electromagnetic spectrum that are not powered by pulsars previously detected by the Fermi-LAT as pulsating gamma-ray signals, which includes 6 Fermi PWNe and 7 Fermi PWN associations. We report the analysis of 58 total regions of interest and provide all firm and tentative detections along with their morphological and spectral characteristics. There are 11 unidentified gamma-ray sources that we classify as firm PWN counterparts, which doubles the PWN population detected by the Fermi-LAT, and 22 gamma-ray sources that are PWN candidates. This will represent a catalog of Fermi-LAT PWNe, named the Fermi-LAT PWN catalog, or 1PWN.
Understanding the PWN population and the interactions that take place are essential for identifying how relativistic particles are injected into the ISM, how they contribute to replenishing the Galactic CR population, and whether they are responsible for local enhancements in the electron-positron flux. For two newly-detected PWNe for which multiwavelength data exist, we apply developed emission models in order to expand our understanding of PWN evolution and hence the underlying particles. The gamma-ray data are combined with available multiwavelength data and compared to the intrinsic properties of the associated systems, such as the supernova explosion energy and pulsar characteristics, in order to establish basic energetic and evolutionary trends for the PWN population.
Eagle, Jordan, "The Pursuit for Gamma-ray Emitting Pulsar Wind Nebulae with the Fermi-Large Area Telescope" (2022). All Dissertations. 3103.
Author ORCID Identifier